<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>flex</title>
<style>
.father{
width: 300px;
height: 300px;
background-color: aqua;
display: flex;
justify-content: center;
align-items: center;
}
.son{
width: 200px;
height: 200px;
background-color: red;
}
</style>
</head>
<body>
<div class="father">
<div class="son">
</div>
</div>
</body>
</html>运行结果
